Actually not that much - depending on how much you are earning. Under the auto entrepreneur scheme total taxes are 23% including their version of prsi if you are earning under 32,000 p.a. A company director with standard tax credits and with PRSI at S1/J1 earning 32,000 here will pay 1,000 a year less than in France under AE. The benefits that you get though, for the extra 1,000 include an excellent health system, pension and services and no need for VHI.
If we were going just for a year or so, then one could, technically, stay off the books in France and stay on the Irish books. That would make it difficult though for anything like medical or anything unexpected. Also even for renting you need to show your annual tax returns, and you would end up being a foreigner rather than integrating...